Recording media such as DVDs (Digital Versatile Discs) on which works such as movies and music are digitally recorded have become prevalent in recent years. In order to prevent illegal copying of content a CSS (Content Scrambling System) has been introduced into the DVD standard. In the CSS, information unique to a DVD medium is recorded thereon, and a title key is generated from this information and information held by a playback device. The generated title key is used to decrypt encrypted content recorded on the DVD medium, and the resultant content is played (see Japanese Patent Application Publication No. 2003-37589).
On the other hand, content distribution systems that use a Digital Rights Management (DRM) system are also becoming common. In DRM, a license is distributed separately to encrypted content. The playback apparatus acquires the license from a specific acquisition destination (such as a specific server apparatus) that is stored in advance. The license includes a license key and a usage condition, and the encrypted content is decrypted using the license key and the resultant content is played in accordance with the usage condition.
As capacity of recording media for recording content continues to grow, it is envisioned that such large-capacity recording media will be distributed in the market place by means of retail sale or the like, with a plurality of contents recorded on any one such recording medium.
However, there are cases in which different contents recorded on any one such recording medium are subject to respectively different playback control management. Such cases include, for example, when a plurality of contents whose copyright holders bear no association with each other exist together on the recording medium, and when content whose usage is restricted according to a playback restriction and content whose usage is restricted according to a playback count exist together on the recording medium. Consequently, there is a necessity in such cases for the content recorded on the recording medium to be able to be played and also be appropriately protected from illegal usage.
In view of the stated problem, an object of the present invention is to provide a content playback apparatus, a content playback method, a computer program, a key relay apparatus, and a recording medium that are effective in enabling a plurality of contents that are subject to respectively different playback control management to be played and also be protected from illegal usage.